Optical Absorption Intensity Research Articles

Entrapment of phenol red pH indicator into polyaniline sol-gel

Optical pH sensors offer a promising alternative method over the existence pH electrochemical sensor and other. Due to ability to achieve high performance, electrical passive operation, simplicity and price effectiveness. Recently, significant research efforts have been devoted to pH sensors for the detection of pH variation in high resolution short range changes. It becomes important to consider ways to heighten the sensitivity of the indicator by improving combination of the material and simple method of sensor fabrication. Effort has been put in studying the fabrication and the sensitivity of film towards pH range in physiological application. Most optical sensors consist of an indicator which is immobilized in a polymer matrix. In this research, polyaniline act as a sol - gel matrix to support pH sensitive indicator molecules which is phenol red. Polyaniline has been found to be versatile functional material which is the most suitable organic material to act as a matrix in aqueous medium and capability to sense on pH changes. The combination between polyaniline with phenol red will enhance the sensitivity of the sensor. The sensing capabilities of the device in term its optical absorption intensity with different pH values were explored. Besides that, simpler and low cost methods was prepared and developed. Through the final investigations, it was found that the phenol red immobilized in a polyaniline film on a portion of fiber optic developed by deposited for 4 layers at thickness is 88.46 nm, withdrawal speed with 15 mm/s and re-cladded length is 15mm/s is the best optimized parameters.

(Invited) Hexagonal Boron Nitride Epilayers

As a member of the III-nitride wide bandgap semiconductor family, BN has received much less attention in comparison with other nitride semiconductors. The stable phase of BN synthesized at any temperature under ambient pressure is hexagonal. Due to its wide bandgap (> 6 eV) and layered structure, hexagonal BN (h-BN) is an ideal platform for probing fundamental 2D properties of wide bandgap semiconductors. In this talk, a brief overview of the synthesis and electrical and optical properties of wafer-scale h-BN epilayers will be presented [1-7]. It was shown that the unique 2D structure of h-BN induces exceptionally high density of states, large exciton binding energy and high optical absorption and emission intensity. By growing h-BN under high V/III ratios, epilayers exhibiting pure free exciton emission have been obtained [4]. Photocurrent excitation spectroscopy results directly provided a room temperature bandgap value for h-BN in between 6.4 and 6.5 eV and the free exciton binding energy (Ex) of 0.73 eV [5]. Layer-structured B-rich BGaN alloys, heterostructures, and quantum wells have also been successfully grown and their properties will be discussed. Thermal neutron detectors fabricated from 100% B-10 enriched h-BN epilayers of thicknesses exceeding 50 mm have attained the highest detection efficiency to date among solid-state detectors at about 58% [6, 7]. These solid-state neutron detectors have become increasingly desirable for a wide range of applications from fissile materials sensing to well logging, because 3He gas detectors are inherently bulky, require high pressurization and high voltage application, slow response time, and expensive. It is our belief that h-BN will lead to many potential applications from deep UV optoelectronics, radiation detectors, to novel layered-structured photonic and electronic devices. [1] R. Dahal, J. Li, S. Majety, B.N. Pantha, X. K. Cao, J. Y. Lin, and H.X. Jiang, Appl. Phys. Lett. 98, 211110 (2011). [2] S. Majety, J. Li, X. K. Cao, R. Dahal, B. N. Pantha, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 100, 061121 (2012). [3] H. X. Jiang, and J. Y. Lin, Semicon. Sci. Technol. 29, 084003 (2014). [4] X. Z. Du, J. Li, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 106, 021110 (2015); 108, 052106 (2016). [5] T. C. Doan, J. Li, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 109, 122101 (2016). [6] A. Maity, T. C. Doan, J. Li, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 109, 072101 (2016). [7] A. Maity, S. J. Grenadier, J. Li, J. Y. Lin, and H. X. Jiang, Appl. Phys. Lett. 111, 033507 (2017) and J. Appl. Phys. 123, 044501 (2018).

Ag nanoparticles in compound metal oxide semiconductors: Syntheses and characterizations

Thermal annealing of Ag-Cu bi-layer thin films on silica-glass substrates either in air or in oxygen environment has led to the formation of novel composite materials (Ag nanoparticles in compound metal oxide semiconductors). Optical absorption and electron microscopy results have confirmed the presence of Ag nanoparticles in oxide semiconductor materials upon annealing. Drastic reductions of the optical absorption intensity in samples annealed at higher temperatures in different atmospheres are explained as a result of thermal growth of the compound metal oxide semiconductor phases. In particular, X-ray diffraction and photoelectron spectroscopy measurements reveal the phases of mixed oxides in the annealed samples. Various experimental measurements discussed here corroborate well with the observed optical results.

Optical Properties of Silver Nanoclusters Synthesized in Surface-Grafted Polyacrylic Acid at Different Grafting Densities

Fluorescent silver nanoclusters immobilized on a plastic substrate are obtained by photoinduced template synthesis using polyacrylic acid chemically grafted to the substrate surface as a template. The electronic absorption and fluorescence spectra of nanoclusters are studied depending on the polyacrylic acid grafting density. It is found that the optical absorption and fluorescence intensities of nanoclusters monotonically increase with increasing grafting density. The position and shape of the absorption and emission spectra almost do not change. The higher the polymer template grafting density, the higher the fluorescence stability of samples during storage at room temperature.

Rhodamine-B absorption and fluorescence enhancement in the near field of gold nanoparticles in an acrylate-based polymer matrix

We describe the preparation of polymer microstructures doped with Rhodamine B organic dye and study the effect of a pinned gold-nanoparticle plasmon resonance on the optical properties of this dye in an acrylate-based polymer matrix. We find that the optical absorption and fluorescence intensity of Rhodamine B in the polymer matrix are enhanced under plasmon resonance.

Оптические свойства нанокластеров серебра, синтезированных в поверхностно-привитой полиакриловой кислоте при разных плотностях прививки

AbstractFluorescent silver nanoclusters immobilized on a plastic substrate are obtained by photoinduced template synthesis using polyacrylic acid chemically grafted to the substrate surface as a template. The electronic absorption and fluorescence spectra of nanoclusters are studied depending on the polyacrylic acid grafting density. It is found that the optical absorption and fluorescence intensities of nanoclusters monotonically increase with increasing grafting density. The position and shape of the absorption and emission spectra almost do not change. The higher the polymer template grafting density, the higher the fluorescence stability of samples during storage at room temperature.

Electronic structures and optical properties of Ce-doped anatase TiO<sub>2</sub> with oxygen vacancy

<sec> The crystal structures, defect formation energy, electronic structures and optical properties of oxygen vacancy and/or Ce-(co)doped anatase TiO<sub>2</sub> are investigated by using density functional theory plus <i>U</i> calculations. </sec><sec> The calculated results indicate that lattice distortion induces the enhanced octahedral dipole moment in Ce doped TiO<sub>2</sub> crystal when introducing oxygen vacancy into the lattice of the TiO<sub>2</sub> crystal, which is effective for separating the photo-excited electron-hole pairs; meanwhile, compared with the valence band of pure TiO<sub>2</sub> and TiO<sub>2</sub> mono-doped separately with Ce and oxygen vacancy, the valence band of TiO<sub>2</sub> co-doped with Ce and oxygen vacancy broadens drastically, which is mainly contributed from the electronic states of Ce 5d, Ti 4s and O 2p in the valence band shifting toward the lower energy direction. As a result, Ce doped TiO<sub>2</sub> with oxygen vacancy is beneficial to the mobility of photo-generated carriers in TiO<sub>2</sub>. Similarly, the anti-bonding states also move toward the lower band energy direction, which are formed by the mixture of Ce 4f, Ce 5d, Ti 3d, and O 2p orbits in the conduction band. Due to these shifts, the energy gap of Ce and oxygen vacancy codoped TiO<sub>2</sub> is narrowed to 2.67 eV with the emerge of the occupied impurity energy levels near Fermi level. Because of the above-mentioned excellence features, the absorption spectra for doped systems exhibit remarkable red-shift, especially, the intensity of optical absorption of TiO<sub>2</sub> co-doped with Ce and oxygen vacancy in the visible region and the infra-red region are obviously stronger than those of the Ce mono-doped TiO<sub>2</sub>. </sec><sec> When introducing oxygen vacancy into the Ce-doped system, the calculated conduction band energy edge position changes from −0.27 eV to −0.32 eV, which implies that the reducing power of the conduction band edge of TiO<sub>2</sub> is remarkably enhanced. More fascinatingly, the calculated band energy edges for the Ce and oxygen vacancy codoped TiO<sub>2</sub> can satisfy the basic requirement for water splitting under visible light irradiation.</sec><sec> In conclusion, Ce and oxygen vacancy co-doped system can effectively strengthen the photo-catalytic activity of TiO<sub>2</sub> and improve the utilization of the solar light; and our calculated results provide a powerful theoretical basis for the applications of the Ce and oxygen vacancy co-doped anatase TiO<sub>2</sub> in visible-light-driven water splitting in the future research. </sec>

Optimizing nanoscale morphology and improving carrier transport of PCDTBT-PCBM bulk heterojunction by cyclic carboxylate nucleating agents

Abstract In this work, four cyclic carboxylate commercial nucleating agents, bicyclo [2.2.1] heptane-2,3-dicarboxylic acid disodium salt (HPN-68L), sodium salt of hexahydrophthalic acid (HHPA-Na), sodium benzoate (Be-Na) and calcium salt of hexahydrophthalic acid (HPN-20E) were respectively added into poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′ benzothiadi-azole)] (PCDTBT)-[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend. Atomic force microscopy (AFM) and UV–vis measurements indicate that the addition of carboxylic acid sodium salts can effectively optimize the morphology of active layer, decrease the phase domain size and increase the optical absorption intensity of PCDTBT-PCBM blends. The PCDTBT-PCBM-additive ternary devices were fabricated and found that adding carboxylic acid sodium salts can improve the hole mobility, balance the hole and electron mobility and finally increase the power conversion efficiency (PCE). Fixed the additive content as 5%, the modulation ability of the bicyclic dicarboxylic acid sodium salt HPN-68L is best, monocyclic dicarboxylic acid sodium salt HHPA-Na comes second, monocyclic carboxylic acid sodium salt Be-Na is worst. The addition of carboxylic acid calcium salt HPN-20E has no effects on the morphology and optical absorption intensity of the PCDTBT-PCBM blend, and the photoelectric properties of PCDTBT-PCBM-HPN-20E ternary device decreases in comparison with those of pristine PCDTBT-PCBM binary device. The modulation ability of cyclic carboxylate is related to its surface free energy and its location in the PCDTBT-PCBM blend. HPN-68L locates in the interfacial region between PCDTBT and PCBM, other cyclic carboxylates locates in the PCBM. Our finding suggests the addition of cyclic carboxylic acid sodium salts can be a facile approach to optimize the morphology and increase the electrical properties of organic materials for future development of organic photovoltaic devices.

Electroic and optical properties of germanene/MoS2 heterobilayers: first principles study.

First principles calculations have been performed to investigate the structural, electronic, and optical properties of germanene/MoS2 heterostructures. The results show that a weak van der Waals coupling between germanene and MoS2 layers can lead to a considerable band-gap opening (53meV) as well as the preserved Dirac cone with a linear band dispersion of germanene. The applied external electric filed can not only enhance the interaction strength between two layers, but also linearly control the charge transfer between germanene and MoS2 layers, and consequently lead to a tunable band gap. Furthermore, the reduction in the optical absorption intensity of the heterostructures with respect to the separated monolayers has been predicted. These findings suggest that the Ge/MoS2 hybrid can be designed as the device where both finite band gap and high carrier mobility are required.

Combined Effect of Uniaxial Strain and Magnetic Field on the Exciton States in Semiconducting Single-Walled Carbon Nanotubes**Supported by the National Natural Science Foundation of China under Grant No 11304378, and the Fundamental Research Funds for the Central Universities under Grant No 2017XKQY093.

The exciton states of semiconducting carbon nanotubes are calculated by a tight-binding model supplemented by Coulomb interactions under the combined effect of uniaxial strain and magnetic field. It is found that the excitation energies and absorption spectra of zigzag tubes (11,0) and (10,0) show opposite trends with the strain under the action of the magnetic field. For the (11,0) tube, the excitation energy decreases with the increasing uniaxial strain, with a splitting appearing in the absorption spectra. For the (10,0) tube, the variation trend firstly increases and then decreases, with a reversal point appearing in the absorption spectra. More interesting, at the reversal point the intensity of optical absorption is the largest because of the degeneracy of the two bands nearest to the Fermi Level, which is expected to be observed in the future experiment. The similar variation trend is also exhibited in the binding energy for the two kinds of semiconducting tubes.

Intervalence charge transfer transition of Co2+-Ti4+ ion pair in α-Al2O3:Co,Ti crystal

A new optical absorption band centered at 356 nm was observed in Co/Ti co-doped synthetic corundum in ultraviolet (UV) region while it doesn't exist in corundum single doped with cobalt or titanium. It is featured with high optical absorption intensity, full width at half maxima (FWHM, greater than 3000 cm−1), strong polarization along the metal ion-metal ion direction, which is consistent with the optical characteristics of intervalence charge transfer transition (IVCT). We propose that the 356 nm absorption band is generated by IVCT of Co2+-Ti4+ heteronuclear ion pair whose formation mechanism would be discussed briefly in this paper. Co2+-Ti4+ was found for the first time in corundum and is the second heteronuclear ion pair discovered in corundum in addition to the known Fe2+-Ti4+.

Supramolecular self-assembled carbon nitride for the degradation of tetracycline hydrochloride

Graphitic carbon nitride microspheres photocatalyst (CN-MCA) was prepared through supramolecular self-assembly with post-heating treatment, which starts from the combination of the raw materials melamine and cyanuric acid. The as-prepared samples were characterized in detail by X-ray diffraction, Fourier transform infrared spectroscopy, new high-resolution field-emission scanning electron microscopy, specific surface areas analysis, UV–Vis diffused reflectance spectrum, photoluminescence spectrum, and thermal analysis. The structural characterization results reveal that the as-prepared CN-MCA has the same chemical structure as CN-M, but appears as microspheres with nanoporous surfaces. Compared to the CN-M, CN-MCA microspheres exhibit higher specific surface areas, stronger optical absorption and lower PL intensity, which allow more active sites, more effective visible-light harvesting and more efficient migration rate of photogenerated charge. Consequently, we observed that CN-MCA microspheres exhibit higher photocatalytic activity in the photodegradation of tetracycline hydrochloride under visible light irradiation. Moreover, the degradation efficiency of tetracycline hydrochloric acid under 2 h of visible light irradiation was 80.54% when the dosage of CN-MCA was 1.0 g/L; the initial concentration of the tetracycline hydrochloride solution was 10 mg/L; and the initial pH was 7.

Energy Band Gap Dependence of Valley Polarization of the Hexagonal Lattice

The origin of valley polarization of the hexagonal lattice is analytically discussed by tight binding method as a function of energy band gap. When the energy gap decreases to zero, the intensity of optical absorption becomes sharp as a function of k near the K (or K′) point in the hexagonal Brillouin zone, while the peak intensity at the K (or K′) point keeps constant with decreasing the energy gap. When the dipole vector as a function of k can have both real and imaginary parts that are perpendicular to each other in the k space, the valley polarization occurs. When the dipole vector has only real values by selecting a proper phase of wave functions, the valley polarization does not occur. The degree of the valley polarization may show a discrete change that can be relaxed to a continuous change of the degree of valley polarization when we consider the life time of photo-excited carrier.

Influence of the number of layers on ultrathin CsSnI3 perovskite: from electronic structure to carrier mobility

Inorganic halide perovskites have attracted great attention in recent years as promising materials for optoelectronic devices, with ultrathin inorganic halide perovskites showing excellent properties and great potential applications. Herein, the intrinsic electronic and optical properties of ultrathin cesium tin tri-iodide (CsSnI3) perovskite with a varying number of layers are explored using first-principles calculations. The results reveal that ultrathin CsSnI3 is a direct band gap semiconductor, and the band gap continues to increase to 1.83 eV from 1.28 eV as the number of layers is reduced to one layer from the bulk. By decreasing the number of layers, the effective mass of ultrathin CsSnI3 increases, and the optical absorption intensity along the x and y directions shows that the linear dichroism becomes stronger and stronger. Furthermore, the carrier mobilities (µ) can be predicted, and they show obvious in-plane anisotropy. The µ of the electrons is higher than that of the holes, and the electron mobility along the y direction is higher than that along the x direction. The layer thickness does not distinctly influence the µ. The difference in the atomic orbital distribution has the nature of obvious anisotropy in ultrathin CsSnI3. This work suggests that ultrathin inorganic perovskite could be a potential candidate for future nano-optoelectronic devices.

DFT + U predictions: structural stability, electronic and optical properties, oxidation activity of BiOCl photocatalysts with 3d transition metals doping

This paper described a comprehensive DFT + U investigation on the general trends in structural stability, electronic and optical absorption properties, photocatalytic activity of BiOCl doped with 3d transition metals (TMs = Sc, V, Cr, Ti, Fe, Co, Ni, Cu, Zn). We find that it is rather difficult for Sc, V, Ti, Ni atoms to substitute Bi into BiOCl crystal lattice in experiments due to their positive formation energies, but the negative formation energies for Cr-, Mn-, Fe-, Co-, Ni-, Cu-, Zn-doped BiOCl systems exhibit the thermodynamic structure stability. Most of TMs doping could narrow the band gap of BiOCl and lead to the changes in conduction band minimum and valance band maximum as well as the formation of several impurity energy levels within the forbidden band of BiOCl, achieving the photoactivity improvement and simultaneously maintaining the stronger redox potential. With 3d TMs doping, the optical absorption intensity of BiOCl around 350 nm increased and exhibited a redshift to the different extents, in good agreement with reported experimental data. Our theoretical calculations should provide meaningful guidance for the experimentalists to design and develop more thermodynamically stable and highly effective visible light response photocatalysts.

Optical absorption intensity analysis using Judd-Ofelt theory and photoluminescence investigation of orange-red Sr2SiO4: Sm3+nanopigments

The Orange-red emitting Sr2SiO4:xSm3+ (x = 0.01–0.09) nanopigments for white light emitting diodes (w-LED's) were prepared by low temperature solution combustion route. Systematic investigations on structural and photoluminescence properties were done with respect to activator concentration (Sm3+). The Judd-Ofelt (JO) intensity parameters that are very significant for the evaluation of laser and luminescent materials are calculated based on the quantitative absorption spectra. This approach for calculating JO parameters are particularly important since the proportional relation between absorption and emission intensities are considered. JO intensity parameters (Ω2, Ω4 and Ω6) were calculated for the sample Sr2-xSmxSiO4 (x = 0.03) for which the emission observed was maximum. These parameters followed the trend Ω2 > Ω6 > Ω4. The visible emission spectrum and JO parameters indicate that the structural environment surrounding the rare earth ions is centrosymmetric in nature. The effect of Sm3+ ion doping concentrations on the luminescent behaviour were investigated in detail using non-radiative energy transfer mechanism. Branching ratio and emission cross section are critical parameters in laser design which in our case are found to be 67% and 3.82 × 10−22 cm2 respectively for the transition 4G5/2 → 6H7/2. Thus, the phosphor can be potentially used for modelling of laser systems and red component as well may be utilised for white light emitting diodes in solid state lightning applications.

Performance enhancement of quantum dot sensitized solar cells under TiO2 nanotube arrays membranes optimization

One-dimensional single crystalline TiO2 nanotube arrays with different length are prepared, and transferred onto the FTO glass substrate with different concentration of Ti-precursor. The relationships between the concentration of Ti-precursor and the optical properties, as well as the photovoltaic performance of the as-prepared solar cells have been investigated. The optical absorption intensity is obviously enhanced and optical absorption edge is expanded to 800 nm for the CdSe/CdS/TiO2 NTs solar cells. In addition, 20 μm - CdSe/CdS/TiO2 NTs solar cells with 0.1 M Ti-precursor have the great photovoltaic conversion efficiency of 4.18%. The excellent photovoltaic performance is attributed to the suitable TiO2 connection layer from 0.1 M Ti-precursor and length of TiO2 NTs, which greatly enhances the electron-hole generation and charge transfer performance in the solar cells. Finally, the photovoltaic efficiency of the as-fabricated solar cells can be further enhanced to 4.51% through the ZnS passivation layer deposition.

Electronic and optical properties of Zr, N mono-doped and co-doped anatase TiO2: first-principles calculations

The growth conditions, crystal structural, electronic, optical and photocatalytic properties of undoped, N-, Zr mono-doped TiO2 and four kinds of Zr/N co-doped TiO2 (Zr–N1, Zr–N2, Zr–N3 and Zr–N4) with different Zr and N co-doped positions were investigated by first-principles calculations. It is found that N substituted preferentially for O under Ti-rich conditions. While Zr substituted preferentially for Ti under O-rich conditions, and has the lowest formation energies (−4.56 eV) due to Zr having the same valence electron distribution as Ti. And, co-doped samples prepared in the experiment may contain all co-doped modes; owing to the formation energies of them being very close under Ti-rich or O-rich conditions. On the other hand, the optical absorption threshold and the optical absorption intensity of Zr–N1, Zr–N2 and Zr–N4 co-doped TiO2 are more enlarged than the N mono-doped and Zr–N3 co-doped TiO2, due to the smaller carrier effective mass and the curved and wide impurity level (IL) appearing in the band gap, which not only increase the carrier mobility and reduce the electron–hole recombination, but also reduces the electronic transition energies. Thus, Zr–N1, Zr–N2 and Zr–N4 co-doped configurations can explain the mechanism of visible light absorption and photocatalytic activity enhancement for co-doped TiO2 and give a good explanation of the previous experimental observation.

Enhanced optical absorption and photocatalytic activity of anatase TiO2 through C[sbnd]Nd-codoped: A DFT+U calculations

The electronic and optical properties are investigated using density functional theory plus U approach in CNd monodoped and codoped anatase TiO2. The calculated results indicate that C dopant can enhance the intensity of optical absorption and Nd dopant can extend the optical absorption range into the whole visible spectrum in CNd-codoped anatase TiO2, and the Nd 4f states can effectively reduce the recombination of photo-excited electron-hole pairs thus achieving higher visible light photocatalytic activity for hydrogen production by water splitting than pure TiO2. Moreover, we also study the effects of doping concentration and impurity distance in CNd-codoped anatase TiO2 system, finding that the higher doping concentration, the stronger absorption activity, and absorption activity increases with the shortness of impurity distance due to the assemblage of impurity states.

Effect of SiO2-doping on photogenerated cathodic protection of nano-TiO2 films on 304 stainless steel

In this study, SiO2-TiO2 composite films were prepared on 304 stainless steel (SS) by a sol-gel method and dip-coating technology. The impact of doping SiO2 on the microstructure and photoelectrochemical performance of the films was investigated. The results demonstrated that pure TiO2 film was composed of anatase and rutile. Doping the film with SiO2 suppressed the phase transformation of anatase to rutile and decreased particle sizes of the films. SiO2 also reduced fluorescence intensity of the composite films, inhibiting the recombination of electrons and holes. Optical absorption intensity of the films first increased and then decreased with increasing SiO2. The corrosion potential of the coated 304SS in 3.5% NaCl in the dark increased along with SiO2 content. Under illumination, however, the 304SS with 10% SiO2-TiO2 film behaved the lowest corrosion potential and smallest charge transfer resistance. Further SiO2 addition caused an amorphous film and suppressed light absorption, resulting in decreased photoelectrochemical performance.